A method of retrieving a mobile platform from a tank having a hatch and at least partially filled with a non-conductive, energetic substance includes configuring the mobile platform to include at least a retrieval system disposed at least partially on an enclosure. The retrieval system includes at least: a primary tether connected to a buoyant body and to the enclosure, and a secondary tether connected to the buoyant body and to the enclosure. The method further includes: predetermining a buoyant body retrieval zone within the tank, and positioning a released buoyant body within the buoyant body retrieval zone by using the primary tether. The method also includes retrieving the primary tether by using the buoyant body; using the primary tether to release the secondary tether; and inserting a retrieval member through the hatch to retrieve the buoyant body, the primary tether, and/or the secondary tether.